replace or repair??(head)

i have a 93 xj with the 4.0L automatic with 192,500 miles on the odo. it smokes blue smoke really bad especially when i wheel. anyways i am wondering if i should take the head thats on there to a local shop and have them fix it and whatever other problems it has. or should i go with a head from here? http://cgi.ebay.com/ebaymotors/ws/e...332081&sspagename=ADME:B:WNA:US:1123&viewitem= i think i could do the valve seals my self but i think the head gasket is bad and who know what else. id rather fix the whole thing or replace it.

anyways thanks for yalls help in advanced.

If you're removing the head, I'd have the head and the block checked to see if their straight. Also, have the head checked for cracks. If your's is good, I'd go with it. Personally, I'd want to have a replacement head checked to see if it was straight or had any cracks before putting it on.

The only reason I'd go for a new head out of the gate would be if you could get one that was better flowing and provided alittle performance boost. Atleast that's my $.02.

at that mileage, the piston rings are worn too, likely the main reason it burns oil.
the whole motor should rebuilt

X2 with Drip. Better to just replace the whole engine than to spend alot just to put a new head on an old engine.

92DripCherokee said:

at that mileage, the piston rings are worn too, likely the main reason it burns oil.
the whole motor should rebuilt

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i hope the rings arent bad. im not too engine inclined, but how can i measure the rings and if they are bad? is it just a visual things or using a feeler guage or what?

also how do i check the block? or does a shop need to do that? sorry for the newb questions. i can do just about everything else i just get uneasy when it comes to engine stuff. any good sources online for engines or should i get my old engine rebuilt?

thanks again!! :wave1:

For starters, a compression gauge can simply be screwed into a spark plug port, and tell you real fast if the valves aren't sealing properly, or the rings are allowing compression to escape. Pull out the fuel pump relay so the engine can't fire, thread in the guage, and turn the motor over, look for a peak value. If you find a low value (below 120), squirt some oil into that cylinder and recheck it. if the compression increases, its worn piston rings


If you decide to rebuild it, no doubt you'll eventually need a machinist. You can check some tolerances yourself, but they're going to recheck them anyway before they do any machining.
Ring gap actually is checked with a feeler gauge, and is adjusted by filing the ends of the ring.

At that mileage, chances are the cylinders will get overbored to some standard oversize, and a piston/ring set will be selected to match.

im going to have the machine shop mess with the head i have now. it will cost about the same as getting a new one off line. i will have to check with the compression tester before i take the head off later this week so i will do that. i hope i dont have to rebuild the engine but what ever needs to be done so i dont have to mess with it smoking and leaking is fine with me.

thanks again and if there is any more advice from anyone let me know.

In general, if it smokes when you start it cold or when decelerating (like going downhill without giving it any gas but still in gear) it's valve seals. If it's warmed up and smokes when your on the gas accelerating it's the rings.

i couldnt tell you if its smoking down hill or accelerating. usually if im wheeling (which i crawl and go slow on trails) or sitting a a stop light is when i can tell. the place i bought it from originally said it was the valve seals, but at this point im just going to get the whole head worked on.

Before doing partial rebuilds, you need to assess total condition of the motor. Compression test as suggested earlier. What about your oil pressure? It is an indication of bearing wear. If it's getting low, you may need new bearings too. Piston rings can be replaced relatively cheaply as long as the head is off. Clearance between the pistons and cylinders can also be calculated to determine that new pistons/overbore may not be needed. And con rod / main bearings can be retorqued for extra insurance.

you may want to save that money for the head and look for a good used motor than rebuild yours into a stroker if you dont know any of the history its likely had terrible or total lack of maintence. was the oil real clean when you bought it, like they changed it cause it looked crappy. you dont read much on here about these engines burning oil